Surface composition of Pt-Pd alloys treated in hydrogen

Szabó, András; Paál, Z.; Szász, András; Kojnok, J.; Fabian, D.J.

doi:10.1016/0169-4332(89)90161-x

Cited by 9 publications

(5 citation statements)

References 25 publications

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“…The theory of metal alloys predicts surface Pd enrichment and was confirmed by Auger electron spectroscopy (AES) of films and powders [27]. This was also observed by Soft X-Ray Emission Spectroscopy of two PdPt foils (containing 15 or 30% palladium) [28]. Pd enrichment was also reported for a disperse PtPd catalyst supported on ␤-zeolite [29]: its hydrogenation activity increased parallel to the Pd content.…”

Section: Introductionmentioning

confidence: 61%

Palladium-platinum powder catalysts manufactured by colloid synthesis

Veisz

Tóth

Teschner

et al. 2005

Journal of Molecular Catalysis A: Chemical

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Palladium, platinum and PdPt bimetallic colloidal particles were prepared in atomic ratios of 4:1, 1:1 and 1:4 by the reduction of K 2 PdCl 4 and/or K 2 PtCl 4 in the presence of cationic surfactant, tetradecyltrimethylammonium bromide (C 14 TABr). The nanoparticles in the "as prepared" state were characterized by TEM, EDS and XPS, UPS, permitting to determine their mean particle size, bulk and surface composition. The bulk composition of the bimetallic samples determined by EDS was close to their nominal value, while XPS indicated Pt enrichment near to the surface. All samples in the "as received" state contained surface oxide impurity and contained carbon impurities. The monometallic samples contained considerably more C as the bimetallic ones. A quasi-in situ H 2 treatment at 473 K in the electron spectrometer resulted in cleaner metals, containing less carbon and oxygen, as shown by XPS and UPS.

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Section: Introductionmentioning

confidence: 61%

Palladium-platinum powder catalysts manufactured by colloid synthesis

Veisz

Tóth

Teschner

et al. 2005

Journal of Molecular Catalysis A: Chemical

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“…Surface segregation induced by thermal treatment under hydrogen 20,30 atmosphere was observed for Pt-Pd alloys. Szabo et al 30 used a model taking the top five surface layers into account to estimate the influence of hydrogen absorption on the surface composition of Pt 0.7 Pd 0.3 alloys. They predicted an increase in Pd surface segregation.…”

Section: And Thementioning

confidence: 95%

Unraveling the Formation of Core−Shell Structures in Nanoparticles by S-XPS

Bernardi

Fecher

Alves

et al. 2010

J. Phys. Chem. Lett.

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The combination of the surface sensitivity of X-ray photoelectron spectroscopy (XPS) with the high flux and variable photon energy excitation of Synchrotron radiation (S-XPS) is used to probe the atomic distribution of bimetallic nanoparticles. Based on the energy dependence of the photoemission differential cross section of core level photoelectrons, we propose a methodology to monitor the formation and to evaluate sizes of the core-shell structure. We have successfully applied it to unveil the mechanism involved in the atomic rearrangement of thermally treated Pt 0.7 Pd 0.3 nanoparticles. SECTION Nanoparticles and Nanostructures

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“…Heat treatment of a similar system (Pd-Pt foils) at 770-800 K in hydrogen caused surface Pd enrichment, as determined by soft X-ray emission spectroscopy (SXES) [38]. This was relatively more marked with 15% Pd (15% → 35-40%) than with a sample containing 30% Pd (30% → 35-40%).…”

Section: Xps and Upsmentioning

confidence: 99%

“…Photoemission studies with syn-chrotron radiation pointed also to Pt enrichment in the first subsurface layer [39]. Szabo et al [38] pointed out also the possible role of subsurface hydrogen [40] in promoting this separation. Heat treatment contributed to leveling off these differences.…”

Section: Xps and Upsmentioning

confidence: 99%

Palladium-platinum powder catalysts manufactured by colloid synthesis

Győrffy

Tóth

Bartók

et al. 2005

Journal of Molecular Catalysis A: Chemical

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Unsupported Pd, Pt and PdPt bimetallic catalysts were prepared in different atomic ratios using methods of colloid chemistry. They were characterized by XPS, UPS and TEM. Four subsequent treatments with O 2 and H 2 up to T = 603 K were applied in the preparation chamber of the electron spectrometer and before the catalytic runs. Platinum strongly hindered the oxidation of palladium in the bimetallic samples indicating an alloying of the two components. The H 2 treatment after O 2 led to rather clean metals. These treatments up to 603 K decreased the Pt enrichment near to the surface found by XPS, destroying presumably the Pt islands on the surface of a Pd-rich matrix. The particle composition approached thus a homogeneous metal mixture. The catalytic behavior was tested in the hydrogenative ring opening reaction of cisand trans-methyl-ethylcyclopropane (MECP) at 373 K. The product ratios 2-methylpentane/3-methylpentane (2MP/3MP) and 2-methylpentane/n-hexane (2MP/nH) were used to characterize the ring-opening pattern of the samples. The bimetallic catalysts revealed higher activity and completely different selectivities than the monometallic Pt and Pd. Moreover, the 2MP/3MP ratio from trans-MECP and 2MP/nH ratio from cis-MECP increased as the surface Pt enrichment decreased. PdPt catalysts were cleaner than Pd or Pt, their activity higher and selectivity closer to random CC rupture, due, very likely, to the presence of active Pd-Pt ensembles.

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Surface composition of Pt-Pd alloys treated in hydrogen

Cited by 9 publications

References 25 publications

Palladium-platinum powder catalysts manufactured by colloid synthesis

Palladium-platinum powder catalysts manufactured by colloid synthesis

Unraveling the Formation of Core−Shell Structures in Nanoparticles by S-XPS

Palladium-platinum powder catalysts manufactured by colloid synthesis

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